1. Field of the Invention
The present invention relates to a lens barrel capable of both lens driving using a driving source and lens driving using a manual operation.
2. Description of the Related Art
Japanese Laid-open Patent Application No. Hei 2-253214 proposes a built-in focusing motor type of lens barrel which is arranged to allow a photographer to substantially serially perform an automatic focusing operation and a manual focusing operation without the need to perform a special switching operation.
The arrangement of the switching mechanism disclosed in Japanese Laid-open Patent Application No. Hei 2-253214 will be described below in brief. Although it is known that when a vibration wave motor is not driven, the rotor of the vibration wave motor is in pressure contact with the stator thereof and held by a large frictional force, the disclosed switch mechanism makes use of this nature of the vibration wave motor. The switching mechanism utilizes a differential mechanism and is arranged to enable switching between the output of the vibration wave motor and the output from a manual operation ring without the need for a special operation, thereby allowing the photographer to perform automatic focusing and manual focusing substantially in series.
FIG. 11 shows the arrangement of the switching mechanism. The arrangement shown in FIG. 11 includes a mount 301 for permitting attachment and detachment of the lens barrel to and from a camera body, a back lid 327 attached to an internal-diameter portion of the mount 301, a fixed tube 330 attached to the mount 301 and serving as a structure part connected to a guide tube 303 which supports a focusing lens 305, the fixed tube 330 further serving to form the external appearance of the lens barrel, and the guide tube 303 fixed to the fixed tube 330 and a motor unit body 331 by screws or the like. The internal peripheral portion of the guide tube 303 is maintained in sliding contact with the external peripheral portion of a focusing-lens tube 304 which holds the focusing lens 305. The guide tube 303 has a plurality of cams 303a for causing the focusing lens 305 to move forward and backward. A plurality of rollers 306 are mounted on the focusing-lens tube 304 in such a manner as to project radially from the external peripheral surface of the focusing-lens tube 304, and the external peripheral surfaces of the respective rollers 306 and the end faces of the corresponding cams 303a are held in sliding contact with each other. The motor unit body 331 is fixed to the fixed tube 330 and the guide tube 303 by screws or the like. Elements 309 to 319 are the constituent parts of a motor unit.
The shown arrangement also includes a ring-shaped stator 312 which serves as a vibrator, and a rotor 313 which is maintained in pressure contact with the stator 312. The rotor 313 rotates about the optical axis of the lens barrel by a vibration of the stator 312. The arrangement also includes a vibration absorber 311 for preventing the vibration of the stator 312 from being transmitted to the outside, a disk spring 310, a pressure adjusting ring 309, and a vibration absorber 314 for absorbing the vibration of the rotor 313. A communication ring 315 supports the rotor 313 and the vibration absorber 314 on its one end surface, and is maintained in contact with the external peripheral surfaces of at least three rollers 317 on the opposite side face. The rollers 317 are respectively supported on a roller ring 316 in such a manner as to be rotatable about axes which pass through an intersection point of the optical axis in a plane perpendicular to the optical axis. The movement of each of the rollers 317 along the rotational axis thereof is restricted by a washer 318. The internal peripheral side of the roller ring 316 is fitted onto the motor unit body 331. A manual-operation input ring 319 is supported on the motor unit body 331 in such a manner as to be rotatable about the optical axis, and is maintained in abutment with the external peripheral surfaces of the respective rollers 17.
A toothed portion 319a is formed around the external periphery of the manual-operation input ring 319, and the toothed portion 319a is meshed with a toothed portion 332a formed around the internal periphery of a manual operation ring 332 so that the manual-operation input ring 319 and the manual operation ring 332 can rotate integrally. The manual operation ring 332 is fitted onto the fixed tube 330 and the motor unit body 331 in such a manner as to be supported rotatably about the optical axis. A focusing key 307, which is fixed to the roller ring 316 at its one end, extends through an opening 331a formed in the motor unit body 331 to control the rotation of the rollers 306 about the optical axis. The lens barrel also includes an electrical circuit board 328 which executes control of a motor and other associated elements.
The operation of the above-described arrangement will be described below. However, since the operational principle of the motor is known, the description of the operation of the motor is omitted, and the following description will refer to only the operations of the essential parts of the arrangement.
When electrical power is supplied to vibrate the stator 312, the rotor 313, the vibration absorber 314 and the communication ring 315 integrally rotate about the optical axis. Then, forces are produced which cause the respective rollers 317 in contact with the communication ring 315 to rotate about their mounting axes. Since the manual-operation input ring 319 is frictionally held by a side face of the motor unit body 331, the rollers 317 roll in contact with the side face of the manual-operation input ring 319, and the roller ring 316 which rotatably supports the rollers 317 rotates about the optical axis. The amount of rotation of the roller ring 316 is selected to be 1/2 of the amount of rotation of the rotor 313. The amount of rotation of the roller ring 316 is transmitted to the focusing lens 305 and the focusing-lens tube 304 by the focusing key 307 via the rollers 306. The rollers 306 are engaged with the cams 303a formed in the guide tube 303, so that as the focusing key 307 rotates, the rollers 306, the focusing-lens tube 304 and the focusing lens 305 move along the optical axis while rotating about the optical axis, thereby effecting automatic focusing.
Since the internal-diameter toothed portion 332a is meshed with the external-periphery toothed portion 319a of the manual-operation input ring 319, as the manual operation ring 332 is manually rotated, the manual-operation input ring 319 is rotated about the optical axis. The rotational force of the manual-operation input ring 319 acts as a force which causes the rollers 317 to rotate about their respective rotational axes. During this time, since the communication ring 315, the rotor 313 and other associated elements are nonrotatably held by the frictional force acting between the rotor 313 and the stator 312, the roller ring 316 rotates at a rotational speed which is 1/2 of the rotational speed of the manual operation ring 332 as described above. The rotation of the roller ring 316 is transmitted to the focusing lens 305 via the focusing key 307, thereby effecting manual focusing.
However, in the related-art mechanism described above, during focusing, it is possible to effect only serial switching between the automatic focusing operation and the manual focusing operation, and the angle of rotation of the manual operation ring 332 and the angle of rotation of the rotor of the vibration wave motor are associated with the movement of the focusing lens 305 in the same relationship at all times. More specifically, if the manual operation ring 332 is caused to make one rotation, the roller ring 316 makes a 1/2 rotation to move the focusing lens 305. During automatic focusing, if the rotor of the vibration wave motor makes one rotation, the roller ring 316 similarly makes a 1/2 rotation to move the focusing lens 305.
In practice, if a photographer is to perform manual focusing, particularly in the case of a focusing operation which requires a large angle of rotation of the manual operation ring 332, the photographer must perform the operation of rotating the manual operation ring 332 to some extent and, after having shifted his/her hold on the lens barrel, rotating it to a further extent. As a result, the photographer cannot perform a rapid manual focusing operation, so that he/she misses a photographic opportunity.
Incidentally, a lens barrel which allows automatic focusing and manual focusing to be serially performed without a special operation is disclosed in U.S. Pat. No. 5,052,781 and U.S. patent application Ser. No. 013,331 (filed on Feb. 4, 1993).